The so-called positive type, photosensitive resin which is insoluble by nature in an aqueous alkali solution, but is liable to be photodecomposed by an actinic radiation as, for example, ultraviolet rays and made to soluble form, is in general far excellent in resolving power than those of negative type photosensitive resinous compositions and hence is widely used as etching resist in the preparation of printed circuit boards, integrated circuit and the like. Among the known positive type photosensitive resinous compositions, the most common member is a resinous composition comprising an alkali soluble novalak resin added with a quinone diazido compound. However, since the base material is a novalak resin prepared by a condensation polymerization technique, there are wide fluctuations of the properties of the resin products and since the softening point is considerably high despite of a comparatively lower molecular weight of the resin, there is a drawback of excessive brittleness of the resist film prepared. Furthermore, it is generally required to add a quantity of quinone diazido compound and therefore, there is a marked decrease in sensitivity of the resulted film to a far lower level as compared with those of chlorinated rubber negative type photoresists.
To cope with the same, attempts have been made to add to an alkali soluble novalak resin with a dihydroxy compound incorporated with a quinone diazido sulfonyl group ( see Japanese Patent Application Kokai No. 182632/83) or with a condensation product of bisphenol type compound and quinone diazido sulfonyl chloride (see Japanese Patent Application Kokai No. 203434/83). In these attempts, indeed the sensitivity of the resist film has been somewhat increased, but the inherent drawbacks possessed by novalak resin have not been improved.
There is an another approach wherein a quinone diazido compound is admixed with an acrylic resin which is a copolymer of monoolefinic unsaturated compound and .alpha., .beta.-ethylenically unsaturated carboxylic acid and has a number average molecular weight of 500 to 10,000, in place of novalak resin (see Japanese Patent Application Kokai No. 43451/83). However, such composition has not been practically used because of various problems involved as, for example, difficulties in having good mechanical properties of the resist film and uniform film performance and in having good control of alkali development. This system is characterized in that the used quinone diazido compound is not soluble in an aqueous alkali solution (and soluble in an organic solvent), but when exposed to ultraviolet rays and converted, via ketene, to an indene carboxylic acid, thus formed carboxylic acid is soluble in an aqueous alkali solution. However, the photodecomposition of said quinone diazido compound is carried out effectively only with the help of ultraviolet rays having an absorption maximum at around 400 nm and therefore, it is unable to expect a high resolving power with other rays having an absorption maximum at more shorter range than the same. Various other positive type photosensitive resinous compositions have likewise been known as described , for example, in Japanese Patent Publication No. 2696/81 and Japanese Patent Application Kokai No. 17445/85, in which use is made of polymer having ortho nitrocarbinol ester group; Japanese Patent Application Kokai Nos. 126236/80 and 141422/86, in which the secondary photolysis reaction is generated by utilizing an acid produced by the first photodecomposition reaction, thereby rendering the resin to its soluble form and the like. However, in the former, there is a deficiency in the photosensitivity of the resin film and in the latter, a deficiency in the time stability of the resinous composition. Thus, none of the heretofore proposed compositions have been practically used. It is, therefore, an object of the invention to provide a novel positive type photosensitive resinous composition which is based on a resin having excellent flexibility and adhesion properties and which is excellent in storage stability and capable of being exposed to a variety of light sources, e.g, U.V. light having an absorption maximum at around 200 nm to U.V. light having an absorption maximum at around 400 nm, and hence is excellent in resolving power when exposed to a light with a shorter wave range.